1. Field of the Invention
This invention relates to a flow control device which causes fluid pressure in a secondary or controlled fluid line to vary in a prescribed manner in response to pressure changes in a primary or controlling gas line. Thus, the controlling gas controls or modulates flow through the secondary fluid line. The controlled fluid may be either a gas or a liquid.
2. Description of the Prior Art
The demand for more energy efficient engines and appliances has enhanced the need for more flexible flow control devices. For example, gasoline engines are turning to fuel injection for more precise matching of fuel flow over wide ranges of engine requirements. This, in turn, requires a sophisticated flow control device which can sense key engine parameters and resolve them into a mechanical technique of metering fuel. Likewise, boilers and other heating appliances are turning toward load following flow control devices which automatically reduce fuel comsumption as demand decreases and vice versa.
Automatic flow control devices have three common features: (1) a device to regulate fluid pressure or flow, (2) a mechanism to operate that device, and (3) a control means to cause the mechanism to operate in a prescribed manner.
One relatively common flow control device is an air loaded regulator. This device uses a diaphragm or piston to separate the fluid being controlled from the controlling air. Controlling air pressure placed on one side of the diaphragm is balanced by the controlled fluid pressure on the other side of the diaphragm. A change in controlling air pressure causes a corresponding response by the controlled fluid.
There are applications when it is necessary that the controlling air pressure be higher than the desired controlled fluid pressure. In such instances, some device must be used between the source or controlling air pressure and the regulator to reduce the air pressure. Likewise, there are applications which require that a given change in controlling air pressure result in an entirely different change in controlled fluid pressure. For example, it may be desired that a 2:1 change in controlling air pressure result in a 4:1 change in controlled fluid pressure. Such refinements require advanced and unique designs in flow control devices.